JP2003227400A - Temperature control device for air/fuel ratio sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize an early activation of an air/fuel ratio sensor without generating a thermal shock by controlling a calorific power by presuming a thermal transition of a protection means of the air/fuel ratio sensor. <P>SOLUTION: The air/fuel ratio sensor 6, 7 are provided with a heater 15 for imparting heat for activating a sensor element 16; and a protector 17 for protecting the sensor element 16. The controller 10 presumes a temperature of the protector 17 and judges that the presumption temperature arrives at a predetermined value at which wetted state is released. The controller switches the heater 15 to the previous heating state until the presumption temperature of the protector 17 arrives at a predetermined value and switches the heater 15 to the heating state having a larger calorific power than that of the previous heating state after it arrives at the predetermined state. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature control device for an air-fuel ratio sensor of an internal combustion engine.

[0002]

2. Description of the Related Art An air-fuel ratio sensor is widely used to detect the exhaust air-fuel ratio of an internal combustion engine and accurately perform feedback control of a fuel supply amount to a target value.

This air-fuel ratio sensor is not activated when the temperature of the exhaust system is low, such as immediately after the engine is started, and the air-fuel ratio cannot be detected accurately in this state. In order to activate the air-fuel ratio sensor early, an electric heater is provided inside the air-fuel ratio sensor, and the heater is energized and heated at low temperature,
The air-fuel ratio sensor is warming up.

However, if condensed water in the exhaust system is adhered to the air-fuel ratio sensor during heating by the heater, the sensor element of the air-fuel ratio sensor may crack due to thermal shock.

Therefore, JP-A-8-15213 and JP-A-2-15213
According to Japanese Patent Publication No. 001-41923, the temperature of the exhaust pipe is detected, such as immediately after the engine is started, to determine the wet state, and the time delay until the heater is activated is set, or a weak current is applied, The constant heating by the heater is performed after the water is removed, thereby preventing the air-fuel ratio sensor from cracking.

[0006]

However, the exhaust pipe temperature does not always accurately reflect the wet state of the air-fuel ratio sensor, and in particular, a protective metal protector is provided outside the air-fuel ratio sensor. With the arrangement, the temperature of the metal protector changes later than the temperature transition of the exhaust pipe. For this reason, if this protector is exposed to water, especially when it is frozen below freezing, and if the heater is heated with a constant current before it completely evaporates due to exhaust heat, etc., the melted water from the protector will be detected. When touching the element, the sensor element may suddenly change its temperature,
It breaks due to thermal shock.

The present invention has been proposed to solve such a problem. By estimating the temperature transition of the protection means of the air-fuel ratio sensor and controlling the operation of the heater, the present invention can avoid thermal shock. The purpose is to enable early activation of the air-fuel ratio sensor.

[0008]

SUMMARY OF THE INVENTION A first invention is an air-fuel ratio sensor for an internal combustion engine, comprising a heating means for applying a heat quantity for activating the sensor element and a protection means for protecting the sensor element. In the above, the means for estimating the temperature of the protection means, the means for determining that the estimated temperature has reached a predetermined value at which the water-exposed state of the protection means is released, and the estimated temperature for the protection means are the predetermined value. Switching means for switching the heating means to a preheated state until reaching a predetermined value, and to a heating state having a larger calorific value than the preheated state after reaching the predetermined value.

In a second aspect based on the first aspect, the temperature estimation means determines the temperature of the protection means based on the amount of heat received from the exhaust gas after the engine is started and the amount of preheat from the heating means. presume.

In a third aspect based on the first or second aspect, the temperature estimating means corrects the estimated value of the temperature of the protecting means according to the intake air temperature at the time of starting the engine.

According to a fourth aspect of the present invention, in the first to third aspects of the present invention, in the preheating state of the heating means, the heat generation amount is set so that the sensor element is not cracked even when it is exposed to water.

[0012]

In the first aspect of the invention, the temperature of the protection means, which is in the vicinity of the sensor element and can accurately reflect the wet state of the sensor element, is estimated, and the heating means is used until the wet state is released. Since it is preheated and switched to a heating state in which the amount of heat generated is larger after release, it is possible to reliably prevent the sensor element from cracking when it is rapidly heated while it is exposed to water, while enabling early activation of the sensor element. Become.

In the second aspect of the invention, the temperature is estimated based on the amount of heat from the exhaust gas actually received by the protection means after the engine is started and the amount of heat from the preheating of the heating means, so that the water-containing state can be accurately determined. Can be done.

In the third aspect of the invention, the temperature of the protection means largely depends on the intake air temperature, which is the environmental temperature when the engine is started. Therefore, by correcting the estimated value of the initial temperature based on the intake air temperature, A more accurate temperature estimation is possible.

In the fourth aspect of the invention, even if the sensor element is exposed to water during preheating, the amount of heat generated is small, so that the sensor element is not cracked by thermal shock, and the temperature rise of the sensor element is promoted in that state. You can

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is an engine body, 2 is an intake pipe, 3 is an exhaust pipe, and an intake temperature sensor 4 for detecting an intake temperature is provided in the intake pipe 1. A catalyst 5 for purifying the exhaust gas is provided in the exhaust pipe 3, and air-fuel ratio sensors 6 and 7 are installed upstream and downstream thereof for detecting the exhaust air-fuel ratio, respectively.

Fuel is supplied to the engine main body 1 by the fuel injection valve 8, and a controller 10 is provided for controlling the supply amount of the fuel so as to attain a target air-fuel ratio according to the operating condition.

Further, as shown in FIG. 2, the controller 10 controls each exhaust sensor 6 immediately after starting the engine at low temperature.
In order to activate 7 early, the energization to the electric heater 15 provided inside each exhaust sensor 6, 7 is also controlled.

An air-fuel ratio sensor 6 attached to the exhaust pipe 3,
Since 7 has the same structure, only one is shown, but the heater 15 is arranged in the central cavity of the sensor element 16,
Further, a protector 17 in the form of a metal cylinder is arranged outside the sensor element 16 as a protection means with a certain gap from the surroundings. The protector 17 has many small holes,
The exhaust gas comes into contact with the sensor element 16 through the small hole.

In the controller 10, as signals representative of an operating state, the controller 10 outputs a rotation speed signal from the engine crank angle sensor 11, a throttle opening signal from the throttle opening sensor 12, and an engine cooling water temperature sensor 13. Together with the cooling water temperature signal of the exhaust air-fuel ratio sensor 6, 7, the air-fuel ratio signal of the exhaust gas upstream and downstream of the catalyst from the exhaust air-fuel ratio sensor 6, 7, the intake air temperature signal from the intake air temperature sensor 4, etc. The amount is controlled, and heating control for the air-fuel ratio sensors 6 and 7 is performed.

Now, the energization control of the heater 15 by the controller 10 will be described with reference to the flowchart of FIG. It should be noted that this flow is repeatedly executed at regular time intervals.

When the engine is started in step S1, it is determined in step S2 whether the engine cooling water temperature or the oil temperature is equal to or higher than a predetermined value. When the engine temperature is sufficiently high so that the air-fuel ratio sensors 6 and 7 are not exposed to the condensed water of the exhaust gas, the process proceeds to step S6, and the energization duty value of the heater 15 is controlled to the maximum state.

However, when the engine cooling water temperature and the oil temperature are not sufficiently high in step S2, step S3
Then, the heater 15 is energized to a low duty value by the preheating control to perform gentle heating.

When the heater is energized while the condensed water is condensing inside the protector, the temperature of the sensor element 16 rapidly rises,
At this time, when the dewed water is melted, comes into contact with the sensor element 16 and is exposed to water, the sensor element 16 is cracked due to thermal shock. Therefore, first, heating is performed slowly with a heat generation amount that does not cause a thermal shock.

It is necessary to accurately estimate the temperature state of the protector 17 in order to maximize the energization of the heater 15 after the condensed water of the protector 17 is surely evaporated. Therefore, in step S4, the protector inner wall temperature of the air-fuel ratio sensors 6 and 7 is estimated.

The temperature of the protector 17 basically depends on the intake air temperature when the engine is started, and after the engine is started, the temperature changes depending on the heat received from the heater preheat by the low duty control and the heat received from the exhaust gas. I will do it.

Therefore, the protector inner wall estimated temperature TMPPRO is calculated as follows.

Now, assuming that the basic protector temperature is TMPBASE, the intake air temperature correction coefficient KPROTM, the starting intake air temperature STRTAN, and the basic intake air temperature (20 ° C) KPROTH, when KPROTH <STRTAN, TMPPRO = TMPBASE KPROTH ≥ STRTAN, TMPPRO = TMPBASE-KPROTH x STRTAN The influence of the intake air temperature at the time of start changes greatly at a predetermined basic intake air temperature of 20 ° C, and when the intake air temperature is low, correction is performed according to the temperature, so TMPPRO is the lower the intake air temperature. It will be a small value. On the other hand, when the intake air temperature is higher than the basic intake air temperature, no correction is made.

Next, the basic protector temperature TMPBASE is
Assuming that the basic protector temperature 1 corresponding to the temperature change due to heater preheating is TMPBASE1, the basic protector temperature 2 corresponding to the temperature change due to exhaust gas is TMPBASE2, and the weighting factors KAPRO1 and KAPRO2 are respectively, TMPBASE = KAPRO1 × TMPBASE1 + KAPRO2 × Request as TMPBASE2. And these basic protector temperatures 1,
Since No. 2 changes according to the elapsed time from engine start, it is updated as follows for each unit time when the flow is repeated.

TMPBASE1 (new) = TMPBASE1 (old) x (1-FCOEF) + PROST x FCOEF TMPBASE2 (new) = TMPBASE2 (old) x (1-0.625 x FCOEF) + PROST x (0.625 x FCOEF) However, FCOEF is a filter Time constant (first-order delay), PROST is the protector inner wall temperature during engine steady operation, for example, engine speed is 2000 rpm, fuel injection pulse width is 50 msec.
The temperature when the protector inner wall temperature has reached a certain value while the above condition continues. The temperature change due to the exhaust gas has a certain delay with respect to the temperature change due to the heater preheating, and is therefore weighted by 0.625.

In this way, the protector inner wall temperature TMPPRO
Once calculated, in step S5, the protector inner wall temperature is
Predetermined value SENH, which is the temperature at which condensed water is sufficiently evaporated
It is determined whether the temperature has risen to ON, and the operations of steps S4 to S5 are repeated until the temperature reaches a predetermined temperature.

The time required to reach the predetermined value SENHON increases as the protector 17 has a lower initial temperature.

If it is determined in step S5 that the protector inner wall temperature TMPPRO has risen to the predetermined value SENHON, the process proceeds to step S6, and the duty value for energizing the heater 15 is switched to the maximum value MAX.

When the engine is stopped in step S7,
Control ends.

Therefore, according to the present embodiment, as shown in FIG. 4, when the engine is started, the air-fuel ratio sensors 6 and 7 are energized by the heater 15, but based on the intake air temperature. When the estimated inner wall temperature of the protector is lower than the predetermined value, the preheating control is performed while keeping the energization amount low.

The temperature of the protector 17 of the exhaust sensors 6 and 7 gradually rises due to the preheating control and the heat of the exhaust gas in the meantime. Even if the protector 17 is contacted with the sensor element 16 in the process where the protector 17 is flooded with condensed water in the exhaust or the condensed water is frozen and evaporates due to this temperature rise, heating by the heater 15 is gentle. Therefore, the sensor element 16 can be prevented from being cracked by a thermal shock.

When the temperature of the inner wall of the protector reaches a predetermined value and it is determined that the evaporation is completely completed, the energization of the heater 15 is switched to a high duty value, and the steady heating of the air-fuel ratio sensors 6, 7 is performed. Is done. At this time,
The sensor element 16 has no risk of being exposed to water, and therefore there is no risk of cracking due to thermal shock.

The temperature of the protector 17 rises after the start due to the amount of heat received by the exhaust gas and the amount of preheating of the heater. The time required for the temperature to rise to a predetermined value is longer as the initial temperature is lower. Since the protector inner wall temperature at engine start is corrected based on the intake air temperature at that time, it can be accurately determined that the protector temperature has reached the predetermined value, and as a result, the air-fuel ratio sensor 6, It is possible to activate the air-fuel ratio sensors 6, 7 early while preventing cracking of the sensor element 16 of No. 7.

It is obvious that the present invention is not limited to the above-mentioned embodiments, and various modifications can be made within the scope of the technical idea thereof.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is also an enlarged view of the main part of the air-fuel ratio sensor.

FIG. 3 is a flowchart showing a temperature control operation of the air-fuel ratio sensor.

FIG. 4 is a timing chart during temperature control of the air-fuel ratio sensor.

[Explanation of symbols]

1 engine body 2 Intake passage 3 exhaust passage 5 catalyst 6 Air-fuel ratio sensor 7 Air-fuel ratio sensor 10 controller 15 heater 16 sensor elements 17 protector

Claims (4)

[Claims] 1. An air-fuel ratio sensor for an internal combustion engine, comprising: a heating means for applying a heat quantity for activating a sensor element; and a protection means for protecting the sensor element, wherein the temperature of the protection means is estimated. Means for determining that the estimated temperature has reached a predetermined value at which the water-covered state of the protection means is released; and preheating the heating means until the estimated temperature of the protection means reaches the predetermined value. The temperature control device for an air-fuel ratio sensor, comprising: a switching means for switching to a heating state in which the amount of heat generated is larger than the preheating state after reaching the predetermined value. 2. The air-fuel ratio according to claim 1, wherein the temperature estimation means estimates the temperature of the protection means based on the amount of heat received from the exhaust gas after the engine is started and the amount of preheat from the heating means. Sensor temperature control device. 3. The temperature control device for an air-fuel ratio sensor according to claim 1, wherein the temperature estimating means corrects the estimated value of the temperature of the protecting means in accordance with the intake air temperature at the time of starting the engine. 4. The temperature of the air-fuel ratio sensor according to claim 1, wherein the temperature of the air-fuel ratio sensor is set such that the sensor element is not cracked when exposed to water in the preheating state of the heating means. Control device.